The invention relates to the production of a composite material comprising a filler and a polymeric material that exhibits antimicrobial properties. The invention relates more particularly to a material having the appearance of marble and/or granite with improved properties as compared to other natural or synthetic materials. Such materials are often used to provide surfaces such as tabletops and countertops that are susceptible to the growth of unwanted bacteria.
Polished natural stones, such as marble or granite and other igneous forms of crystalline silica or siliceous rock, are often used as decorative and functional facing and surfaces in long-lasting construction applications. However, these products require expensive handling in shaping and finishing and are only available from relatively few geographical regions. These factors significantly add to the already high cost of employing such materials. Additionally, due to natural imperfections, cracking and general brittleness can be encountered by builders working with natural stone.
Another issue with natural stone is that it can be quite porous and can absorb liquids that come into contact with it. This tendency to absorb liquid can lead to staining and water marking upon use. Absorbance of liquid can also provide the moist environment that favors bacterial growth.
In an attempt to avoid the problems inherent in natural stone products, various synthetic-filled polymeric compositions have been developed for use in applications such as countertops, floors, and architectural facings. These synthetic materials are commercially available. Typically, these materials incorporate a polymeric resin and inorganic fillers, and are cured using curing systems that are actuated at room temperature or at elevated temperatures. One drawback of these compositions is that they lack aesthetic appeal with consumers that consider the look of natural stone to exemplify high quality and taste.
Accordingly, many attempts have been made to develop products having the pleasing aesthetic appearance of natural products. Certain synthetic products have become available which provide the appearance of natural stone, especially marble and granite, at a fraction of the cost of solid stone. These so-called cultured stone products are man-made molded products generally consisting of resin highly filled with natural aggregate, inorganic particles and/or pigments.
One such product is described in U.S. Pat. No. 3,278,662 to Mangrum. This reference describes a stone-containing tile product which can be mass-produced, and used to avoid the problems that generally face the installer of terrazzo products. The tile product as disclosed therein contains about 7 to about 25 percent by weight of a thermosetting polyester resin, and about 93 to about 75 percent by weight of stone particles. The components are compressed in a mold and cured; the resulting products are rigid in nature and have deficiencies that are similar to those noted with ceramic and marble tile products.
Another procedure commercialized by Breton S.p.A. of Castello di Godego, Italy, and commonly known as the “Breton Stone” process, has found commercial success in this area. In this technology, conventional polyester resin precursors are blended at low weight percentages with aggregate to provide a relatively dry mass of material that is vibro-compacted under vacuum and then cured to yield a rigid tile product. A process used to practice this technology is disclosed by Toncelli in U.S. Pat. No. 4,698,010. A specific polyester resin that can be used in this technology is disclosed by Slocum in U.S. Pat. No. 5,321,055. Other patents related to this technology are U.S. Pat. Nos. 5,264,168; 5,800,752; and 6,387,985.
The growing popularity of artificial stone products has resulted in the increased use of such products in home and business construction. The most common application for artificial stone is as a replacement for solid stone countertops and tabletops. Artificial stone is also used in architectural facings, walkways, home furnishings, patio furniture, decorative stones, indoor and outdoor tile, flooring, wall coverings, mantles, bathroom fixtures, and imitation stone structures.
One thing that all of these uses have in common is that they place the artificial stone in aesthetically important areas and in close proximity to human activity. These are also areas where the growth of bacteria, mold, mildew, and fungus is highly undesirable. Countertops and tabletops are two uses where such growth is especially undesirable given their close proximity to food preparation.
Although these synthetic stone replacements are superior to stone in a number of ways they still possess some of the deficiencies that are inherent in products made from natural stone. One such deficiency is the porosity of natural stone. Natural stone and aggregates thereof are porous and tend to absorb water which can lead to staining similar to that which occurs with natural stone slabs. The water absorbed by the stone particles also provides a moist environment suitable for growth of microorganisms that can stain the product, produce slick and dangerous surfaces, produce unwanted odors, contaminate food, act as a cross-contamination vector, and promote illness.
The porosity and rough surface of natural aggregate has led many producers of artificial stone to add a gel coat to the surface of their products. Although these gel coats add a degree of water repellency to the finished products, they can be damaged from harsh cleaning chemicals and they may not completely seal the underlying porous aggregate.
In short, the increased use of artificial stone products in countertops, tabletops and other areas of high human contact has generated a need for reducing or eliminating the potential for growth of microorganisms on the surface of the artificial stone.
Accordingly, it is an object of the present invention to provide an improved composite material having an appearance similar to that of natural stone that reduces or eliminates the presence of microbes on the surface of the material. It is another object of this invention to provide for such a material in a cost effective manner suitable for widespread commercial use.